The role of a specific vasopressin-secreting pathway in the hypothalamus in adrenal cortical function is being investigated in the rat. It arises in the paraventricular nucleus of the hypothalamus and secretes into the hypophysial portal blood circulation. Glucocorticoids inhibit this vasopressin system. Anatomical and physiological studies are being carried out to determine (1) the nature of the vasopressin pathway to portal blood, (2) its relationship to the pathway to posterior pituitary gland, (3) the site(s) where glucocorticoids act in the brain to inhibit it, (4) the role of vasopressin in the suprachiasmatic nucleus.